The present invention relates to a recording/reproducing head for recording information on magnetic media and reproducing recorded information. The invention also relates to a magnetic recording apparatus using such a recording/reproducing head.
In a magnetic recording apparatus which records a magnetic information mark on a code track of a magnetic recording medium by scanning the medium with a recording/reproducing head, and reproduces information by detecting with this head the magnetic field leaking from the information mark, it is necessary for the head to accurately follow up the track. In order to solve this problem, a track servo method is used in general. The track servo method involves causing a recording/reproducing head to accurately follow up a code track of a magnetic recording medium on which servo burst patterns for track servo are recorded in advance. According to this method, the reproduction of the servo burst patterns with the recording/reproducing head makes it possible to detect the offset (deviation) of the head from the code track. On the basis of the detected offset, it is possible to correct the position of the recording/reproducing head. Such track servo needs an actuator for moving the recording/reproducing head to any track and causing the head to follow up the track. In general, a rotary actuator for turning a swing arm is used. A linear actuator may alternatively be used, but the rotary actuator is used more widely because it enables the configuration of the servo system to be simpler, enabling the magnetic recording apparatus to be smaller and the cost to be lower.
FIG. 6 schematically shows a magnetic recording medium 200 and a recording/reproducing head 204 for use with a rotary actuator. The recording/reproducing head 204 is mounted on a slider 110, which is fitted to the front end of a swing arm 133. During track servo, the swing arm 133 pivots on the axis of the rotary actuator 201 to position the recording/reproducing head 204 on any code track of the recording medium 200.
The prevailing recording/reproducing head is a combined recording/reproducing head, which consists of a recording magnetic head 203 for recording information and a reproducing magnetic head 202 for reproducing recorded information and management information such as addresses. FIG. 8 schematically shows a conventional combined recording/reproducing head. As shown in FIG. 8, the recording/reproducing head 204 is mounted on the rear of a slider 110, which is fitted to the front end of a swing arm 133. The movement (rotation) of a magnetic recording medium 200 in the direction indicated by an arrow shown in FIG. 8 forces air in under the slider 110. The air lifts the slider 110 from the recording medium 200. In the meantime, the swing arm 133 pushes the slider 110 toward the recording medium 200. The lifting and pushing forces counterbalance each other, causing the slider 110 and the recording/reproducing head 204 to float at a predetermined distance from the recording medium 200.
FIG. 9(a) is an enlarged section of the recording/reproducing head 204 shown in FIG. 8. The reproducing magnetic head 202 consists basically of magnetic shields 251 and 252 and a magnetoresistive element 253. The recording magnetic head 203 for recording information consists basically of the magnetic shield 252, a coil 254 and an upper magnetic pole 255. The magnetic shield 251 is formed adjacent to a substrate during the production process and referred to as a lower magnetic shield. The other magnetic shield 252 is formed over the magnetic shield 251 and referred to as an upper magnetic shield.
The lower and upper magnetic shields 251 and 252 of the reproducing magnetic head 202 function to improve spatial resolution by absorbing magnetic fields that leak from the peripheries of the shields and that are not necessary for reproduction. Some of the leaking magnetic fields may be magnetic fields (crosstalk) leaking from the information marks recorded on the code tracks adjacent to a code track from which information is being reproduced. Others of the magnetic fields leaking from the peripheries may be magnetic fields (interference between codes) leaking from the information marks preceding and succeeding a track from which information is being reproduced. For less crosstalk and/or for easier production of the recording/reproducing head 204, it is preferable that the shields 251 and 252 be wider than the spacing of the code tracks.
The electric resistance of the magnetoresistive element 253 of the reproducing magnetic head 202 is changed by the magnetic field leaking from a record mark recorded on the magnetic recording medium 200. By applying a suitable bias to the magnetoresistive element 253, it is possible to detect the existence or nonexistence of a record mark as the amplitude of an electric signal. The magnetoresistive element 253 is more sensitive than the conventional inductive heads and can detect the existence or nonexistence of an information mark. Therefore, the magnetoresistive element 253 is used widely in particular to reproduce information from magnetic recording media on which information is recorded densely. However, because the magnetoresistive element 253 can generate no magnetic field for recording, the separate recording magnetic head 203 is necessary which can generate recording magnetic fields.
The recording magnetic head 203 is basically identical in structure with the conventional inductive heads and needs a lower magnetic pole for pairing with the upper magnetic pole 255. If a lower magnetic pole were separately provided, however, the space between the recording and reproducing heads 203 and 202 would be too large. Therefore, in many common cases, the upper magnetic shield 252 of the reproducing magnetic head 202 is shared also as the lower magnetic pole of the recording magnetic head 203. In fact, the wider the space between the heads 203 and 202, the larger the offset between the tracks followed up by the heads 202 and 203. The offset is caused by the yaw angle made by the use of the rotary actuator. This problem will be explained below in detail.
With reference to FIG. 7, the conventional track servo method during information recording and reproduction will be described with the rotary actuator shown in FIG. 6, the recording/reproducing head 204 shown in FIG. 8, and the magnetic recording medium 200, on which servo burst patterns 220-223 for track servo are recorded in advance. During track servo, as shown in FIG. 7, the reproducing magnetic head 202 reproduces the patterns 220 and 221, and the position of this head 202 is controlled in such a manner that the reproduced patterns 220 and 221 are equal in amplitude. Specifically, the difference between the signals representing the reproduced patterns 220 and 221 is the basis for generating a tracking error signal 226, which represents the offset of the reproducing magnetic head 202 from a track. The position of this magnetic head 202 is controlled in such a manner that the level of the error signal 226 is 0. Hereinafter, the xe2x80x9c0xe2x80x9d level of the error signal 226 will be referred to as a reproducing servo target position 224.
The recording/reproducing head 204 is fitted to the front end of the swing arm 133, which, as shown in FIG. 6, pivots on the axis of the rotary actuator 201. Consequently, the axis of the recording/reproducing head 204 inclines at an angle of xcex8 (yaw angle) with (the line direction of) the code tracks (FIG. 7). If this head 204 is a combined recording/reproducing head as mentioned above, the yaw angle of xcex8 causes the loci described by the reproducing and recording magnetic heads 202 and 203 to differ from each other. The yaw angle is a function of the radius of the magnetic recording medium and the space of D between the heads 202 and 203. The larger the yaw angle or the space of D, the larger the offset between the loci. During information reproduction, if the reproducing magnetic head 202 accurately follows up a code track, the recording magnetic head 203 may follow up any position. During information recording, however, the recording magnetic head 203 needs to accurately follow up a code track.
Japanese Patent Application Laid-Open No. 8-221918 discloses an electric head position correction method as a means for solving the foregoing problem. This method involves setting a recording servo target position 225 during recording, in addition to the reproducing servo target position 224. This is based on the following idea. As shown in FIG. 7, when the reproducing magnetic head 202 follows up a code track m, the recording magnetic head 203 follows up the position offset by xcex94T from the track m. Accordingly, during recording, if the reproducing magnetic head 202 is caused to follow up the position (track mxe2x80x2) offset by xe2x88x92xcex94T from the track m, the recording magnetic head 203 follows up the track m. In order for the reproducing magnetic head 202 to follow up the offset position, it is necessary to carry out track servo in such a manner that, as shown in FIG. 7, the level of the tracking error signal 226 is xe2x80x9cxcex1xe2x80x9d. The practical track servo involves applying a DC offset of xe2x80x9cxe2x88x92xcex1xe2x80x9d to the error signal 226, with the same results. Hereinafter, the level of xe2x80x9cxcex1xe2x80x9d of the error signal 226 will be referred to as the recording servo target position 225. As stated already, the yaw angle is a function of:the radius of the magnetic recording medium. Accordingly, the offset xcex94T between the loci of the reproducing and recording magnetic heads is another function of the radius. In other words, the recording servo target position 225 is still another function of the radius, and it is updated for each recording radius.
The foregoing means positions the recording magnetic head 203 so that this head can accurately follow up a code track during recording. Then the recording magnetic head 203 records information on the code track. The recorded user data is a digital time series signal of xe2x80x9c1xe2x80x9d or xe2x80x9c0xe2x80x9d. Before the signal is recorded, it is modulated or otherwise preprocessed into a record signal. Similarly to the user data, the record signal is a digital time series signal of xe2x80x9c1xe2x80x9d or xe2x80x9c0xe2x80x9d. In accordance with the record signal, a recording drive circuit (not shown) supplies a current to the coil 254, which is shown in FIG. 9(a). This current generates in the upper magnetic shield 252 and the upper magnetic pole 255 a time-changing magnetic field corresponding to the record signal. Specifically, xe2x80x9c1xe2x80x9d of a record signal row is recorded with a positive current supplied to the coil 254. The positive current generates a left-hand (counterclockwise) magnetic field in the loop formed by the upper magnetic shield 252 and the upper magnetic pole 255 shown in FIG. 9(a). xe2x80x9c0xe2x80x9d of the record signal row is recorded with a negative current supplied to the coil 254. The negative current generates a right-hand (clockwise) magnetic field in the loop formed by the upper magnetic shield 252 and the upper magnetic pole 255 shown in FIG. 9(a).
FIG. 9(b) shows the recording/reproducing head 204 as viewed through the magnetic recording medium 200. When the left-hand magnetic field is generated, a magnetic flux leaks from the upper magnetic shield 252 and is absorbed by the upper magnetic pole 255. The magnetic flux generates a magnetic field in the recording medium 200 in the same direction as the medium 200 moves. As a result, a record mark 152-2 magnetized in this direction is formed in the recording medium 200. When the right-hand magnetic field is generated, a magnetic flux leaks from the magnetic pole 255 and is absorbed by the magnetic shield 252. This magnetic flux generates a magnetic field in the recording medium 200 in the direction opposite to the direction in which the medium 200 moves. As a result, a record mark 152-1 magnetized in the opposite direction is formed in the recording medium 200. Thus, the information recorded on the recording medium 200 is recorded as the directions of magnetization of the information marks 152-1, 152-2, etc.
The width (track width) of the information marks 152-1, 152-2, etc. recorded by the conventional recording magnetic head 203 shown in FIGS. 9(a) and 9(b) is determined by the width of the magnetic fields applied from this head 203 to the magnetic recording medium 200. The width of the applied magnetic fields is determined primarily by the width of the upper magnetic pole 255. In order to narrow the tracks by narrowing the information marks 152-1, 152-2, etc., it is necessary to narrow the magnetic pole 255 as well. However, the production of narrow magnetic poles needs expensive processing equipment such as an FIB. In addition, if the magnetic pole 255 is narrow, the magnetic fields that can be output from it may be too low in strength for recording.
Japanese Patent Application Laid-Open No. 3-189905 discloses a magnetic recording method (so-called light-assisted magnetic recording) for recording information on a magnetic recording medium while irradiating the medium with a laser beam emitted from a semiconductor laser, which is mounted on a magnetic head. The irradiation locally heats the recording medium to temporarily lower the coercive force of the heated region of the medium. This is advantageous because (the strength of) the recording magnetic field applied from the magnetic head can be lower than the coercive force of the recording medium.
Japanese Patent Application Laid-Open No. 4-176034 discloses another light-assisted magnetic recording method. In particular, this document discloses a method for reproducing information, which uses a magnetic recording medium including a recording layer made of a ferrimagnetic material having a compensation temperature about room temperature. During reproduction, a reproducing region of the recording layer is irradiated with a light beam to be heated. The heated region is magnified in magnetization. By detecting the magnetic flux leaking from the region magnified in magnetization, it is possible to reproduce information.
Japanese Patent Application Laid-Open No. 6-243527 discloses another light-assisted recording method. In particular, this document discloses a magnetic recording apparatus including a slider on which a magnetic head and a semiconductor laser are fixed. FIG. 2 of the document shows the relationship between a hot write part heated by the radiation of a laser beam and the facing position of the magnetic head. The facing position of the magnetic head is shown inside a high-temperature region.
However, if such a light-assisted recording method is used with a recording magnetic head driven by a rotary actuator, it is conceivable that a yaw angle problem, which will be stated later on, will arise between the semiconductor laser and the recording head.
The present invention has been completed to solve the foregoing various problems with a magnetic recording apparatus including a recording/reproducing head that can be positioned by a rotary actuator. The problems arise if the track spacing is narrowed for higher density.
A first object of the present invention is to provide a recording/reproducing head and a magnetic recording apparatus that can carry out reliable tracking servo in recording information with a magnetic head driven by a rotary actuator.
A second object of the present invention is to provide a recording/reproducing head and a magnetic recording apparatus that can generate a magnetic field having a necessary strength even for densely recording information on a narrow-track magnetic recording medium.
A third object of the present invention is to provide a recording/reproducing head and a magnetic recording apparatus that can record information reliably on a desired track by a light-assisted magnetic recording method with a magnetic head driven by a rotary actuator.
A fourth object of the present invention is to provide a recording/reproducing head and a magnetic recording apparatus that can be driven by a rotary actuator and produced at low cost, and that are suitable for a light-assisted magnetic recording method.
According to a first aspect of the present invention, there is provided a recording/reproducing head for recording information on a magnetic recording medium and reproducing information from the medium. The recording/reproducing head comprises:
a recording magnetic head for applying a magnetic field to a predetermined part of the recording medium, the magnetic head having a pair of magnetic poles;
a laser light source for irradiating at least part of the predetermined part with a laser beam; and
a magnetoresistive element for detecting a magnetic field leaking from a record mark formed by the recording magnetic head, the magnetoresistive element being interposed between the pair of the magnetic poles of the magnetic head.
According to a second aspect of the present invention, there is provided a magnetic recording apparatus comprising:
a magnetic recording medium on which information can be recorded;
a recording/reproducing head for recording information on the recording medium and reproducing the recorded information; and
a rotary actuator for moving the recording/reproducing head relative to the recording medium.
This recording/reproducing head includes:
a recording magnetic head for applying a magnetic field to a predetermined part of the recording medium, the magnetic head having a pair of magnetic poles;
a laser light source for irradiating at least part of the predetermined part with a laser beam; and
a magnetoresistive element for detecting a magnetic field leaking from a record mark formed by the recording magnetic head, the magnetoresistive element being interposed between the pair of the magnetic poles of the magnetic head.
With reference to FIG. 10, the recording principle of the recording/reproducing head according to the present invention and the magnetic recording apparatus including this head will be explained. The pair of magnetic poles of the recording magnetic head of the recording/reproducing head are an upper magnetic shield 101 and a lower magnetic shield 100, which generate a recording magnetic field. The laser light source of the recording/reproducing head radiates a light spot 150 on a magnetic recording medium 140. FIG. 10 conceptually shows the positional relationship between the recording magnetic field and the light spot 150. FIG. 10 also conceptually shows the variation of the coercive force Hc of the recording film of the recording medium with respect to the positions of the recording magnetic field and the light spot. During information recording, the magnetic recording medium is moved in the direction of recording medium movement indicated by an arrow in FIG. 10. If a region where information is to be recorded is irradiated with the light spot 150, the region is heated to form a high-temperature region indicated by reference numeral 151.
It is known that the coercive force Hc of a magnetic recording medium is a function of the temperature T of the medium and expressed by the following expression (1).
Hc=H0(1xe2x88x92{square root over ( )}xcex1T)xe2x80x83xe2x80x83(1)
where H0 is the coercive force in case of inversion only with a magnetic field without heat fluctuation influence (the coercive force at a temperature of 0 K (Kelvin)), and where xcex1 is the characteristic value determined by the recording medium. As apparent from the expression (1), the higher the temperature of the recording medium, the smaller the coercive force Hc. Accordingly, if a temperature distribution exists in the recording medium, the coercive force is smaller in a high-temperature. region, as apparent from the expression (1), and the distribution of the coercive force is as shown by the upper and right graphs of FIG. 10. The coercive force changes reversibly. If the temperature of the recording medium returns to normal, the coercive force is restored to its original value.
The recording-limit coercive force of a magnetic recording medium is defined as the maximum coercive force of this medium at which information can be recorded stably with a recording magnetic field generated from a recording/reproducing head. The present invention uses a magnetic recording medium having a variable coercive force that is higher at normal temperature than the recording-limit coercive force of the medium. The invention also uses a laser light source. The intensity of the laser beam emitted from the light source is adjusted in such a manner that the variable coercive force lowered by a temperature rise is lower than the recording-limit coercive force. As shown by the upper graph of FIG. 10, the high-temperature region 151 represents the range where the variable coercive force is lower than the recording-limit coercive force HCL. Accordingly, information can be recorded in the high-temperature region 151. The intensity of the laser beam can be adjusted in such a manner that the width of the high-temperature region 151 in the track direction is narrower than the widths of the upper and lower magnetic shields 101 and 100. In order for the recording magnetic field to have a magnitude necessary for recording, the widths of the upper and lower magnetic shields 101 and 100 in the track direction may be greater than the width (track pitch) of the code tracks. Thus, by using a magnetic recording medium having a high coercive force at normal temperature, and by recording information in a region of the medium with a laser beam radiated onto this region to lower the coercive force of the region locally and temporarily, it is possible to record information on each code track even if the width of the upper and lower magnetic shields 101 and 100 are greater than the width of the code tracks. The right side of FIG. 10 shows marks (magnetic domains) 152-1 and 152-2 recorded on the recording medium according to this principle. It should be noted that, herein, the track direction means the direction perpendicular to the direction along the tracks, while the line direction means the direction along them.
The width of the upper magnetic pole of the conventional recording magnetic head defines track width. Therefore, for smaller track spacing for denser recording with the conventional recording magnetic head, it was necessary to narrow the upper magnetic pole 255 as shown in FIG. 9(b). This lowered the magnetic field strength that could be output from the recording magnetic head. The lowered field strength was not sufficient for recording. The recording/reproducing head according to the present invention records information in a region of a magnetic recording medium with a laser beam radiated onto the medium to locally lower the coercive force only of this region of the medium on which information is to be recorded. Accordingly, by suitably controlling the intensity of the laser beam or the spot diameter, it is possible to determine the track width independently of the widths of the magnetic poles which generate a magnetic field. This makes it possible to use a recording magnetic head with magnetic poles wider than the track width, making it possible to acquire a sufficient magnetic field strength even if the track spacing is small. In addition, this makes the magnetic head easy to produce. In order to provide a sufficient magnetic field strength to the recording film of a magnetic recording medium during information recording, it is preferable that the width W of the magnetic poles of the recording magnetic head of the recording/reproducing head according to the invention and the width Tw of the record marks recorded on the medium satisfy 2xc3x97Tw less than W.
During information reproduction, a magnetoresistive element detects the magnetic fields leaking from the record marks recorded on a magnetic recording medium. As shown in FIG. 2(b), for example, the magnetoresistive element 111 of the recording/reproducing head according to the present invention is interposed between the upper and lower magnetic shields 101 and 100 of the recording head. Therefore, the upper and lower magnetic shields 101 and 100 improve the spatial reproducing resolution due to the magnetoresistive element 111 by absorbing magnetic fields that leak from the peripheries of the shields and that are not necessary for reproduction. The leaking magnetic fields may be magnetic fields leaking from record marks recorded on the tracks adjacent to a track from which the recording/reproducing head is reproducing information.
The magnetoresistive element 111 is interposed between the upper and lower magnetic shields 101 and 100 of the recording head. Accordingly, the recording magnetic head and the reproducing element are positioned at the same location, particularly in the direction along the swing arm that pivots by means of the rotary actuator. Even if the use of the rotary actuator causes a yaw angle to be formed, the recording magnetic head and the reproducing element have no tracking offset from the code tracks. Therefore, if the recording/reproducing head according to the present invention is mounted on the rotary actuator, it is not necessary to apply an electric offset to a tracking error signal, as was the case with the foregoing prior art. As a result, stable track servo can be realized even if the track spacing is small.
The magnetic recording apparatus according to the present invention includes a recording/reproducing head fitted with a laser light source. The magnetic recording apparatus also includes a rotary actuator and a swing arm, which position the recording/reproducing head at a desired track. The recording/reproducing head includes a recording head and a magnetoresistive element. The recording head, the laser light source and the magnetoresistive element may be mounted coaxially on a slider. In this case, as shown in FIG. 11, the axis Sa of the swing arm forms a yaw angle xcex8 with the center Tc of the track. The laser light source 132 heats a heating-up region 302 of a magnetic recording medium. The upper and lower magnetic shields 101 and 100 apply a recording magnetic field to a region 303 of the recording medium. It is necessary to keep the heating-up region 302 from deviating in the track direction from the region 303. This requirement is met by a relational expression as explained below with reference to FIG. 12. As shown in FIG. 12, the axis Sa of the swing arm of the rotary actuator inclines at the yaw angle xcex8 with the track center Tc of the magnetic recording medium. The emission port 300 of the semiconductor laser 132 has a width Wa. The heating-up region 302 heated by the semiconductor laser 132 has a width Tww in the track direction. The upper magnetic shield 101 of the recording head has a width Ww (=Wwp+Wwm). The distance between the semiconductor laser and the recording head is d. The foregoing requirement is expressed by the following expression (2).
Tww/2+dxc3x97|sin xcex8| less than Wwpxc3x97|cos xcex8|xe2x80x83xe2x80x83(2)
The expression (2) expresses the following condition. A longitudinal half 101a (lower in FIG. 12) of the upper magnetic shield 101 has a vertical length component expressed as Wwpxc3x97cos xcex8. The portion of the shield half 101a that is positioned above the track center Tc in FIG. 12 has a vertical length component expressed as dxc3x97sin xcex8. In order for the half 101a of the recording head to completely cover the heating-up region 302, it is necessary to meet Tww/2+dxc3x97sin xcex8 less than Wwpxc3x97cos xcex8. This leads to the expression (2). A similar conception applies even to a case where the swing arm axis Sa inclines relative to the track center Tc to the side opposite the side to which it inclines in FIG. 11, that is to say, a case where xcex8 is negative. If the lengths of Wwm and Wwp of the shield halves 101a and 101b, respectively, are equal (Wwm=Wwp), the relationship between the other half 100b of the upper magnetic shield 101 and the heating-up region 302 is defined with the expression (2). For Wwm=Wwp, wwp in the expression (2) can be replaced by Ww/2 (Wwp=Ww/2). Because xcex8 in the expression (2) may be negative, the terms sin xcex8 and cos xcex8 in this expression are treated as absolute values. For xcex8 less than 0, if the halves 100 and 101 differ in length from each other (Wwmxe2x89xa0Wwp), Wwp in the expression (2) should be replaced by Wwm. As stated already, the emission port 300 of the semiconductor laser has a width of Wa. The correction coefficient (factor) based on the intensity distribution of radiated light is xcex1. The width of Tww of the heating-up region 302 may be expressed as Tww=xcex1xc3x97Waxc3x97cos xcex8. If the intensity distribution of light accords with Gaussian distribution, xcex1 is about 0.4.
Therefore, by selecting the upper magnetic shield 101, in particular its width Ww, for the yaw angle of xcex8 of the rotary actuator and the width Wa of the emission port 300 of the semiconductor laser in such a manner that the expression (2) may be met, the heating-up region 302, which can be irradiated with a laser beam, can be positioned always within the magnetic field application region 303. This makes it possible to record information reliably on a desired track of the magnetic recording medium even when the rotary actuator and the swing arm move the laser light source and the recording/reproducing head.
In the present invention, in order to easily position the heating-up region 302 within the magnetic field application region 303, it is preferable that the distanced between the light emitting section of the laser light source and the magnetoresistive element be even shorter. The distance of d may be 5 xcexcm or less.